Thermal constraints are critical in industrial systems where customer requirements do not allow for use of fans or other forced air flow for cooling. These constraints are becoming increasingly difficult to satisfy as technology trends are forcing electronic module design in the direction of higher power dissipation and resulting heat output. These technology trends include: (i) replacement of traditional, dedicated-purpose, proprietary ASICs that operate at lower clock speeds with commercially available CPUs that operate and higher clock speeds; (ii) increasingly smaller silicon geometries for CPUs that lead to correspondingly increased leakage currents; and, (iii) increasingly harsh customer environments for installation location of industrial electronic modules, with a desire by customers to increase the allowable ambient temperature specification above 60° C. while silicon packaging techniques for CPUs and the like are forcing a reduction in allowable junction temperatures in which the silicon can operate.
The problem of cooling industrial electronic modules is exacerbated by the fact that industrial electronic system are typically modular, with little or no air flow within or adjacent the modules which limits the effectiveness of traditional heat sinks. Thus, for example, a conventional heat sink, using only convection, located within the module and connected to the CPU is insufficient for cooling. Also, conduction of heat to a cover of each industrial electronic module has been found to be insufficient for cooling due to the lack of air flow around the modules and the desire not to increase the spacing between modules.
As noted above, use of fans or other forced air cooling systems is not satisfactory. In some cases, customer requirements simply do not allow for use of fans. Furthermore, use of fans is undesirable due to reliability problems with the fans and the tendency of fans to draw dust and other contaminants into the electronic module. Other cooling systems such as radiant systems, closed-loop phase change systems, and the like are known, but are space and cost prohibitive and present concerns when used as part of an electrical systems.